In a cylinder block of an internal combustion engine, an oil passage through which oil that is pressurized flows is formed. An oil jet is an apparatus which injects oil supplied from the oil passage, to a piston or a gap between the piston and a cylinder bore, and which thereby cools the piston that has become high in temperature. A conventional oil jet generally used has a mechanism for opening and closing its valve in accordance with oil pressure. Specifically, a body of the valve is biased in a direction acting against the oil pressure by a spring, and the valve is configured to open as a result of the body of the valve separating from a valve seat when a force of oil pressure acting on the body of the valve exceeds the force of the spring. The oil pressure increases with an increase in the revolution speed of the internal combustion engine, whereas because the temperature of the piston increases with an increase in the revolution speed, the above described mechanism can cool the piston by injecting oil in a situation in which the temperature of the piston becomes high and prevent the piston from being excessively cooled by stopping the injection of oil in a situation in which the temperature of the piston is not high.
An oil jet disclosed in the following Patent Document 1 also has a mechanism for opening and closing its valve in accordance with oil pressure. This oil jet has a further mechanism for changing the injection amount of oil in accordance with oil temperature. The mechanism corresponds to a throttle member that is disposed upstream of the valve. A plurality of throttle holes are formed in the throttle member. Fluid resistance of oil acts when passing through these throttle holes, and the magnitude thereof increases with an increase in the viscosity of the oil. Because of this, the flow rate of the oil passing through the throttle holes becomes smaller when the temperature of the oil is low and the viscosity of the oil is high, whereas the flow rate of the oil passing through the throttle holes becomes larger when the temperature of the oil is high and the viscosity of the oil is low. According to such mechanism, when the valve is opened in association with an increase in oil pressure, the injection amount of oil is suppressed because of low oil temperature if it is during the cold condition immediately after an engine start up, whereas the injection amount of oil is increased in association with an increase in oil temperature if it is after completion of a warm up.
In addition, another oil jet is proposed which has a mechanism for opening and closing its valve in accordance with oil temperature as well as a mechanism for opening and closing the valve in accordance with oil pressure. An oil jet disclosed in the following Patent Document 2 has a first mechanism for opening and closing its valve with a normal spring and a second mechanism for opening and closing its valve with a spring made of a shape-memory alloy. According to the first mechanism having the normal spring, the valve is opened when a force of oil pressure acting on a body of the valve exceeds the force of the spring. On the other hand, according to the second mechanism having the spring made of a shape-memory alloy, the valve becomes closed during the cold condition in which the spring is compressed, whereas the valve becomes opened during the warm condition in which the spring is restored to expand. With such mechanisms, both valves are opened to inject oil only when the oil pressure is high and the oil temperature is high.
Alternatively, an oil jet, as with, for example, an oil jet disclosed in the following Patent Document 3, is proposed which can electrically control the execution and stopping of oil injection by driving a body of its valve using a solenoid.